It is known to prepare nitrodiphenyl ethers by reaction of halonitrobenzenes with phenolates in reaction media such as, for example, chlorobenzene, phenol, dimethyl sulphoxide, sulpholane, dimethylformamide, dimethylacetamide, N-methylpyrrolidone or polyethylene glycol. In these reactions, copper is often required as a catalyst (Houben-Weyl, Methoden der organischen Chemie (Methods of Organic Chemistry), volume VI/3 (oxygen compounds I, 1965), p. 86 et seq.). Except in the case of halonitro-compounds which react particularly readily such as, for example, 2,4-dinitrochlorobenzene, fairly high reaction temperatures and long reaction times are generally required to obtain conversions of 60-79% at all. The reaction media mentioned create problems and financial expenses because they must be recovered for ecological reasons.
The preparation of nitrodiphenyl ethers has also already been attempted in the presence of liquid ammonia. At -40.degree. C. in the presence of liquid ammonia, no reaction between para-nitrochlorobenzene and sodium phenolate was observed even after a reaction time of 10 hours; even 2,4-dinitrochlorobenzene which is much more strongly activated gave a yield of only 80%, even when the reaction was carried out with twice the molar amount of sodium phenolate in liquid ammonia at -33.degree. C. (Zhur Org. Khim. 18 (1982), 2321-2327; English translation 1983, 2051-2056).
Surprisingly, it has now been found that nitrodiphenyl(thio) ethers can be prepared from halonitrobenzenes and (thio)phenolates in liquid ammonia at a higher temperature than hitherto expected, even though there was the risk that un der the influence of the ammonia being present at a high concentration halonitrobenzenes would carry out an aminolysis reaction to give nitroanilines. However, the reaction temperatures are considerably less than those which were hitherto thought to be necessary in the presence of the abovementioned reaction media; this is of importance especially with respect to the thermal instability of some nitro-aromatics at higher temperatures in the presence of strong bases.
The manner in which the reaction is conducted according to the invention is clearly superior even to the positive effect, mentioned in European Patent 0,022,387, of phase transfer catalysts which are stable to bases on the rate of the reaction of chloronitrobenzenes with alkali metal phenolates in the abovementioned reaction media.